Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus including the same, which are suitable for a broadcasting television camera, a movie camera, a video camera, a digital still camera, a monitoring camera, and a silver-halide film camera, for example.
Description of the Related Art
In recent years, a zoom lens having a wide angle of field, a high zoom ratio, and high optical performance is required for an image pickup apparatus such as a television camera, a movie camera, a silver-halide film camera, a digital camera, or a video camera. There has been known, as a zoom lens having a wide angle of field and a high zoom ratio, a four-unit zoom lens including a first lens unit having a positive refractive power, a second lens unit having a negative refractive power that is used for zooming, a third lens unit having a negative refractive power that is used to correct image plane variation accompanying zooming, and a fourth lens unit having a positive refractive power that is used for image formation (Japanese Patent Application Laid-Open No. H09-15501 and Japanese Patent Application Laid-Open No. 2004-341237).
In Japanese Patent Application Laid-Open No. H09-15501, there is disclosed a zoom lens having a zoom ratio of approximately 8 and an angle of field of photography at a wide angle end of approximately 87°. In Japanese Patent Application Laid-Open No. 2004-341237, there is disclosed a zoom lens having a zoom ratio of approximately 2.9 and an angle of field of photography at a wide angle end of approximately 94°.
In the four-unit zoom lens having the structure described above, it is relatively easy to achieve the increased angle of field. However, in order to obtain high optical performance in the four-unit zoom lens, it is important to satisfactorily correct a lateral chromatic aberration in the entire zoom range. If an optical material having characteristics of anomalous dispersion is used, the lateral chromatic aberration is satisfactorily corrected with ease. However, even if a lens made of the material having the characteristics of anomalous dispersion is merely used, it is difficult to satisfactorily correct the chromatic aberration. In order to obtain the high optical performance over the entire zoom range in the above-mentioned four-unit zoom lens, it is important to appropriately set the materials of the lenses included in the second lens unit that moves during the zooming.
In addition, in the four-unit zoom lens having the structure described above, the high zoom ratio is relatively easy to achieve, but in order to achieve both the increased high zoom ratio and the reduction in size, it is important to appropriately set the arrangement of the refractive powers of the lenses. In particular, in the four-unit zoom lens having the structure described above, the second lens unit mainly plays a role of changing the zoom. Therefore, it is important to satisfactorily set the lens structure of the second lens unit and the materials of the lenses included in the second lens unit.